91 240, Temp Gauge Pegging [FIXED]

[Rushin]

I finally finished up my engine, trans and interior swap. Not sure what year engine is in the vehicle but I don't think it matters for this issue. It's a 91 240.

On my dash, as long as the cluster has power, the temp gauge pegs. Straight to the top. Unplugging/grounding the temp sensor has no effect. I have continuity at from the coolant temp sensor, all the way to the cluster plug. I've swapped out the voltage regulator on the dash to no avail.

I'm loath to do the compensator bypass, as I've done it on my 1990 240 and the gauge always reads a 1/4 under pegged as the normal temp. I'd like to avoid that on this one as this is my labor of love, haha. Is there anything else I can possibly check or diagnose before I go any farther? I'm guessing it's the compensator board but I think all 3 of the clusters I have, have bad compensator boards lol


Edit: I did the bypass the easy way with a bit of wire on my silver 240, so I moved that wire over to the cluster on my project 240, and it STILL pegs. So it isn't even the compensator. Now I'm more stumped, not less haha

 

[Jack]

If I remember correctly the were two temp sensors … early and late cars

Also not the pegging I came in for

 

[johfraser]

The lead from the gauge to the sensor is shorted to ground somewhere between the two. Thats why shorting or removing the sensor connection makes no difference. You could test this by disconnecting the lead from both the gauge and sensor. Then run a new wire between the two. I guess it is also possible the short is in the dash circuit board.

 

[hiperfauto]

If I remember correctly the were two temp sensors … early and late cars

Also not the pegging I came in for

That only applies to 140/164. '73- 140/164, all 240 and '84-'86 740 all use the same sender.

 

[Rushin]

The lead from the gauge to the sensor is shorted to ground somewhere between the two. Thats why shorting or removing the sensor connection makes no difference. You could test this by disconnecting the lead from both the gauge and sensor. Then run a new wire between the two. I guess it is also possible the short is in the dash circuit board.

I have continuity between the gauge and sensor. I did fix the issue. The compensator board looked okay, but I pulled it and did the internal bypass. After that I swapped the gauge itself with a junk cluster I had lying around and it works like a charm! Now onto my fuel gauge and speedo...